1. Field of the Invention
This invention relates to sensing and locking devices for use, for example, when an elongate moving member is required to be locked in a predetermined position when the elongate moving member has reached that predetermined position.
2. Summary of the Prior Art
In label applicators, for example, it is generally necessary that labels coated with a self-adhesive and carried on a silicone-treated backing strip shall be accurately positioned in a predetermined position within the applicator so that printing can be effected at a precise location on a given label. Detection of the positions of labels on the backing web could readily be effected by photo-sensitive means, but such means involve the use of electrical circuitry and hence the provision of a power source, which is not normally possible in a hand-held applicator. To overcome the difficulty it has been proposed to incorporate in the backing strip notches or other registration devices and by this means it has been possible to construct label applicators with feed devices which ensure correct registration of the labels at a printing station by engagement with the notches at predetermined points as the labels are indexed through the applicator. The cost of such webs is, however, higher than for plain webs with parallel sides and labels abutting one another on one surface of the web.
It is clearly desirable from the cost standpoint to employ label webs of simple form with rectangular or square labels and it is desirable that the position of the labels on the web should be detected by the very small forces generated by the labels themselves in order to arrest them at a predetermined position.
Accordingly an object of the invention is to provide a sensing and locking device which can detect and act on small forces such as those which can be applied by an edge of a label.